1. Field of the Invention
The present invention relates generally to radio-frequency identification (RFID) systems, and in particular relates to systems for and methods of processing RFID-tag signals that improve the readability of such signals by a RFID-tag reader.
2. Technical Background
Radio-frequency identification (RFID) is a remote recognition technique that utilizes RFID tags having information stored therein. The stored information is retrievable via radio-frequency (RF) communication between the RFID tag and a RFID-tag reader. The typical RFID system utilizes a RFID-tag reader, which is often designed to be hand held for the sake of mobility. When the RFID-tag reader is brought sufficiently close to a RFID tag, it can read a digital RFID-tag signal communicated by the tag. RFID systems are conventionally used for inventory management and product tracking in a variety of different industries, as well as in libraries and hospitals. The data encoded into a RFID tag can generally be written at a distance, and some types of REID tags can be re-written multiple times.
There are three main types of REID tags. The first type is a passive RFID tag that has a microcircuit (typically, a digital memory chip) with no internal power supply. The microcircuit includes or is coupled to an antenna. A passive RFID tag is powered by an incoming RF interrogation signal from the RFID-tag reader. The RF interrogation signal provides enough power for the microcircuit to communicate the information stored in the RFID tag to the RFID-tag reader via an electromagnetic RF tag signal from the RFID tag antenna.
The second type of RFID tag is semi-passive, and includes a microchip, antenna, and a small power supply that powers the microchip, allowing the RFID tag to operate and communicate a RFID tag signal without requiring power from the incoming RF signal, leading to a greater read range.
The third type of RFID tag is active and has its own power supply. Active RFID tags generate an outgoing RF tag signal and can respond to RF interrogations from the RF tag reader, or periodically generate their own outgoing RF tag signal.
In reading RFID tags, the RFID-tag reader interrogates the tag many times (e.g., more than 100 times) per second. The RFID-tag reader reads a corresponding RFID-tag signal for each interrogation. If the acquired RFID-tag signal does not correspond to a legitimate digital stream of a standardized protocol and error-checking method, then the acquired RFID-tag signal is identified as a “read error” and discarded. In practice, ambient electronic noise from a variety of sources (typically, machines and devices near the RFID tag or electronic noise in the RF circuitry of the reader) limits the range of the RFID-tag reader and causes many of the RFID interrogations to generate read errors. Other RFID-tag signal impairments can also occur, such as multi-path fading and bandwidth reduction and dispersion, which result in less-sharp rise and fall times. Consequently, only some of the RFID-tag signals are properly read, and the ability to properly read the RFID tag signals decreases with the distance between the RFID tag and the RFID-tag reader.
Improving the RFID reading capability of a RFID system can allow for a greater read range, smaller antenna sizes for the RFID tag, better RFID capability in electronically noisy environments, higher success rate of reading the RFID tag, etc.—all of which improve the RFID system efficiency while reducing system cost and user frustration.